energy
1) Explain Energy
- Amount of work done = energy transferred.
- SI unit for energy is Joules (J).
- The sun is the source of energy for all our energy resources except geothermal, nuclear and tidal.
- In the sun, energy is created through a process called nuclear fusion: hydrogen nuclei are pushed together to form helium.
- The moon is the main source of tidal energy.
- Energy can be transferred between different forms including kinetic, gravitational potential, chemical, elastic potential, nuclear and internal energy as a result of an event or process.
- An object may have energy due to its motion (KE) or its position (PE), and that energy may be transferred and stored.
Kinetic energy:
\[K.E.=\frac{1}{2}mv^{2}\]
Gravitational potential energy: G.P.E = m g h
- Work is done when a force moves something through a distance. The work done is equal to the energy transferred.
work done = energy transferred
Energy type |
What it is |
Example |
Kinetic |
Due to motion |
Moving objects |
Gravitational |
Due to position (height) |
Objects lifted to a certain height |
Chemical |
In chemicals |
Batteries |
Elastic |
Due to stretch |
Elastic band |
Nuclear |
Due to atoms rearranged/split |
Nuclear plant |
Electrical |
Carried by electrons |
Electricity |
Light |
Carried in light waves |
From sun |
Sound |
Carried in sound waves |
From speaker |
2) Conservation of Energy
- Energy cannot be created or destroyed, when work is done, energy is changed from one form to another.
- Example of conversion of energy: A book on a shelf has g.p.e , if it falls of the shelf it will have k.e.
- Due to the processes through which energy transfers take place not being 100% efficient, energy is lost to the surrounding and therefore energy gets more spread out (dissipated).
3) Efficiency:
How much useful work is done with energy supplied
4) Energy Resources
Non-renewable sources of energy: are exhaustible
Type |
Advantages |
Disadvantages |
Fuel: burnt to make thermal energy, makes steam, turns turbine |
Cheap. Plentiful. Low-tech |
Harmful wastes: Greenhouse/pollutant gas |
Renewable sources: are not exhaustible
Type |
Advantages |
Disadvantages |
Wave energy: generators driven by up and down motion of waves at sea. |
No greenhouse gases produced |
Difficult to build |
Tidal energy: dam built where river meets sea, lake fills when tides comes in & empties when tide goes out; water flow runs generator |
No greenhouse gases produced |
Expensive. Can’t be built everywhere |
Hydroelectric: river & rain fill up lake behind dam, water released, turns turbine generator |
Low impact on environment. Energy produced at constant rate |
Few areas in the world suitable |
Nuclear fission: uranium atoms split by shooting neutrons at them |
Produces a lot of energy with very little resources |
Produces radioactive waste |
Wind: windmills are moved by the breeze. They generate electricity from kinetic energy |
No CO2/Greenhouse gases produced |
Few areas in the world suitable |
Solar cells/photovoltaic cells: made of materials that deliver electrical current when it absorbs light Solar Panels: absorbs energy and use it to heat water |
No CO2 produced |
Variable amount of sunshine in some countries |
work and power
- Work done is the same as energy transferred.
- Conservation of energy links GPE, KE and work done.
- Power is the rate of transfer of energy or the rate of doing work.
work done = Force x distance moved in the direction of the force
W = F d = E
W = F d = E
5) Work
- Work is done whenever a force makes something move.
- The unit for work is the Joule (J).
Work Done = Force x Distance moved in the direction of the Force
W = F x D
W = F x D
6) Power
Power is a measure of how quickly work is being done and so how quickly energy is being transferred.
The unit for power is Watts (W)
1 W = 1 J/s
The unit for power is Watts (W)
1 W = 1 J/s
\[P=\frac{E}{t}\]
in simple systems, including electrical circuits